§1.1 Field of the Invention
The present invention concerns transmitting signals. In particular, the present invention concerns the guidance of radio waves through free space, such as for use as an economic, light-weight, substitute for conventional signal cables.
§1.2 Background Information
Conventional cables use a continuous body of conducting material for transmission of electrical signals from an input source to a distant load. This type of a cable, such as a coaxial cable, may be used for direct current (DC), as well as radio frequency (RF) signals. However, such cables become ineffective at higher frequencies due to power loss in the conducting material.
For such high-frequency radio waves (and for optical signals), signal propagation is possible using cables made of continuous dielectric material. Such cables, for example an optical fiber, are referred to as “dielectric waveguides.” However, dielectric waveguides also use a continuous material body to transfer signal power from a source at one end of the waveguide to a distant load (or receiver) at the other end.
Unfortunately, cables and waveguides used for carrying signals have certain disadvantages due to their requirement of having continuous material. Consider, for example, a cable carrying a signal from an antenna in the attic of a home, to a room at the other end of the home. Obstructions such as ceilings/floors and walls must be provided with openings to allow the cable to pass. As another disadvantage, the need for continuous material places a limit on how light the cable may be, or how little material may be used per length of “signal carry”. Finally, the cable may be inadvertently severed or otherwise compromised at any point along its length.
Therefore, it would be useful to allow signals to be “carried” from a source point to a load (or sink) point by a means without the above-mentioned disadvantages of cables and waveguides.
Signals can be also be transmitted through an empty space, using a pair of antennas to transmit and receive radiation. Unfortunately, however, in the process of such signal transmission through an empty space, the signal power is lost in various arbitrary directions. Consequently, only a very negligible fraction of the power of the signal radiation transmitted from the transmitting antenna is collected by the receiving antenna. While this process may be acceptable for information communication between distant points, it is not useful to transfer signal power.
Although the percentage of power transferred through the empty space received may be increased by using large antennas to better focus the radiation in the specific direction between the transmit and receive points, this may only be practical over a limited distance. This is because as the distance is increased, the power received would be reduced with the square of the distance. Furthermore, larger antennas are not practical for many applications. Transmitting signals through an empty space using a pair of antennas to transmit and receive radiation is, by nature, not well suited for directing or guiding the signal. This is because the free-space medium has a natural tendency to spread or diffract the signal.
Therefore, it would be useful to allow signals to be “carried” from a source point to a load (or sink, or reception) point by means without the above-mentioned disadvantages of transmit and receive antennas (and without the above-mentioned disadvantages of cables and waveguides).